In a conventional structure, in disposing a light-receiving element that receives light output from an optical waveguide in front of or at the side of a substrate having the optical waveguide, the light-receiving element may be disposed outside the substrate. According to such a structure, because the light-receiving element is attached to the substrate as an external element, the overall size of an optical device package including the light-receiving element increases.
According to a disclosed technique, a structure in which a chip is mounted on a substrate by flip-chip bonding and an underfill agent fills a gap between the chip and the substrate, a groove formed on the substrate prevents the ingress of the underfill agent (such as adhesive) into an area where the presence of the underfill agent is undesirable (see, e.g., Japanese Laid-Open Patent Publication No. 2003-243444). According to another disclosed technique, a projection formed on an end of an optical waveguide prevents an adhesive from flowing to a reflection surface on the end of the optical waveguide (see, e.g., Japanese Laid-Open Patent Publication No. 2008-145684).
The light-receiving element may be bonded to the surface of the substrate by, for example, an adhesive, instead of being disposed outside the substrate. In such a structure, the light-receiving element can be included within the area of the size of the substrate, enabling a reduction in the size of the package. However, if light emitted from the optical waveguide and incident on the light-receiving element passes through the adhesive containing air bubbles, light is reflected irregularly by the air bubbles. As a result, the quantity of light received by the light-receiving element decreases. If a groove is formed on the substrate to prevent the adhesive from flowing into a light path leading from the optical waveguide to the light-receiving element and the groove cannot be formed as a groove traversing the optical waveguide, the inflow of the adhesive to the light path may be impossible to prevent.